Mark Edinger is the Scientific Advisor for Flow Cytometry at Q2 Solutions. In this episode, he describes recent advances in flow cytometry and what that means for immuno-oncology trials. New instruments, reagents and software are enabling researchers to monitor 30-some markers simultaneously to get a better picture of the tumor micro-environment and the interactions taking place. For example, there's a whole list of new checkpoint inhibitors, like PD-1, CTLA-4, CD-1-52 and a multitude of other CD-47 that have been described, and their ligands on T cells and immune cells, not just T cells, that allows the tumor to actively turn off the host response to the tumor that prevent the tumor from being killed by the immune system. We weren't aware of these, many of these, until we had the tools that allow us to look at many more markers simultaneously. For instance markers of T cell activation have been around for a long time, but that list has expanded remarkably now, and the lists of markers of T cell exhaustion have really expanded as well, and some of those were not discovered until relatively recently, in the last 5 or 6 years. Mark explained how flow cytometry is being used to determine whether a therapeutic is efficacious or not and the benefits that flow to the patient. He stressed, as others in this series have, the importance of early engagement between sponsors and their clinical trials partners. Regular phone calls and direct conversations between scientists help refine the assays to produce the desired result in terms of the information collected from a panel.